Re: Panasonic 27" Squashed Picture


lantel@xxxxxxxxx wrote:

I have a 1992 Panasonic PC-29XF10A 27" TV.

Since about 2 days ago, a ~2" black bar appeared at the bottom of the
picture and the remaining picture on top of that is compressed
(squashed) vertically.

Does anybody have an idea of what components went? And how to figure
out which ones to replace?

Haven't repaired any TV's so I am a bit lost when looking inside of
one, so if anyone can help me in terms of physically locating the area
that went, that would be great.

Also, what's the proper way of discharging TV caps?

The www.repairfaq.org is a great resource of electronics repair
information and explains safety procedures, including how to discharge
capacitors. The most likely capacitor hazard is the picture tube
itself, so don't unplug the thick cable going to the rubber cup on the
side of the tube. Also don't ignore the hazard of the fragile glass
picture tube shattering because TVs tip over very easily, usually
forward.

A local library may carry Sams Photofacts (no apostrophe in "Sams")
repair manuals, but Panasonic sells factory repair manuals for very low
prices.

Your TV may have a bad capacitor in the main power supply, but far more
likely a capacitor in the vertical output section is going bad. To
find the vertical chip, trace the 4 wires leading from the picture tube
yoke (not the small circuit board that plugs into the end of the tube)
to the main circuit board, and look up the part numbers of the chips
near those wires by searching www.nteinc.com, www.bdent.com,
www.alldatasheet.com, www.datasheetarchive.com, or by simply Googleing.
I would replace all the electrolytic capacitors connected to the
vertical chip, but if you need to replace only one, very likely you
want the ramp generator timing capacitor. Any new capacitor must be
rated for at least as much voltage as the original, and its capacitance
value (uF) should be within 20%. Try to get caps rated for 105
Celcius, not the usual 85C. Watch polarity because installing a
polarized cap backwards can cause it to short and go bang.

I hope your desoldering skills are good because you don't want to
damage the circuit board. Use a 30-40W iron (40W is better) with a
very clean tip and narrow (.05-.08" wide) copper desoldering braid.
Cut the braid right after it absorbs solder. If the solder won't wick
up completely, then you either need a more powerful iron (don't exceed
50W), a cleaner tip, or should add fresh 60/40 tin/lead solder and
start over. Practice on a junk board first.

.

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